Sorry to hear about the little scumbags doing that to your son. It's so upsetting especially for younger people whose cars are their pride and joy. As everyone else has said for heavens sakes stick out of a good offer from the insurance, don't whatever you do take what they offer the first few times, as they always try it on.
Your son has a very healthy attitude and that'll serve him well through life and I really do hope it all gets sorted out for him without him ending up massively out of pocket.